Segerman, Anna

Umeå University, Faculty of Medicine, Clinical Microbiology.

2004 (English)Doctoral thesis, comprehensive summary (Other academic)

Abstract [en]

At present, the human adenoviruses (Ads) comprise 51 members, which have been classified into six species (A to F). In general, adenovirus (Ad) tissue tropism or disease patterns vary according to species, although adenoviruses from different species can sometimes cause the same symptoms. The current interest in adenoviruses is partly due to the aim of using them as vectors for gene therapy. Hematopoietic cells are attractive targets for gene therapy and the transductions can be performed ex vivo. However, the most commonly used adenovirus vectors, based on Ad2 or Ad5, are inefficient in their transduction of hematopoietic cells since they attach poorly to these cells. Most Ads, including Ad2 and Ad5, appear to use the coxsackie-adenovirus receptor (CAR) (a component of tight junctions), for attachment to host cells. However, species B Ads do not bind to CAR and several studies have indicated that species B-based vectors would be more suitable for hematopoietic cells. Species B Ads can be further divided into species B1 and B2, which display different tissue tropisms. Species B1 Ads mostly cause acute respiratory infections whereas species B2 Ads have been associated with persistent infections of the kidney and urinary tract. One of the key determinants of tropism is believed to be the initial high-affinity attachment of the virion to host cell fiber receptors. By reciprocal blocking experiments and different ways of characterizing the species B attachment receptors, we have shown that the species B2 serotypes Ad11p and Ad35 and the species B1 serotypes Ad3p and Ad7p also differ in receptor usage. There are at least two different Ad species B receptors. Since one of these receptors appeared to be used by all four serotypes, we designated this receptor sBAR (species B adenovirus receptor). The other receptor appeared to be used exclusively by the two species B2 serotypes and was therefore designated sB2AR (species B2 adenovirus receptor). Binding to sBAR can be abolished by EDTA and restored with Mn2+ or Ca2+, whereas binding (of Ad11p and Ad35) to sB2AR is independent of divalent cations. Furthermore, sBAR appears to be trypsin sensitive whereas sB2AR is not.

We also identified CD46 as a receptor for Ad11p. Even so, CD46 does not appear to be a functional receptor for Ad7p. Both Ad7p and Ad11p attached to CD46-transfected Chinese hamster ovary (CHO) cells more efficiently than to control CHO cells. However, only Ad11p (selectively) infected CD46-transfected CHO cells. Anti-CD46 antibodies inhibited Ad7p and Ad11p from binding to, and Ad11p from infecting, CD46-transfected CHO cells. However, in human cells, anti-CD46 antibodies had an inhibitory effect only on Ad11p binding (~30%) but did not affect Ad7p binding. In binding experiments with EDTA, divalent cations and pretrypsinized cells, Ad11p and Ad7p showed the same pattern in their binding to CHO-CD46 cells as in the previous study. Since Ad7p interacted almost as efficiently with control CHO cells as with CHO-CD46 cells after addition of Mn2+, it seems that Ad7p mainly addressed an endogenously expressed hamster receptor on CHO-CD46, the properties of which resemble sBAR. In addition, Ad3p and Ad7p attach poorly to PBMCs and CD46 is expressed on all nucleated cells. Thus, CD46 appears to correspond to sB2AR rather than to sBAR.

With these differences in receptor usage in mind, we studied the binding and infectious capacity of these species B Ads in various hematopoietic cells. We found that all species B serotypes bound efficiently to CD34+ hematopoietic stem cells (HSCs) and also productively infected HSCs. However, only the sB2AR binding Ad serotypes Ad11p and Ad35 could attach primary PBMCs efficiently. Our results regarding the subsequent steps in infection of PBMCs suggest that both Ad11p and Ad35 enter PBMCs and deliver viral DNA to the nuclei of most PBMC cell types. However, productive infections were only clearly detected in stimulated T-cells (most frequently) and monocytes, whereas Ad infection seemed eclipsed in unstimulated lymphocytes. Replication of Ad DNA seemed seriously impaired in at least T-cells, indicating limited production of infectious particles in PBMCs. The capacity of species C Ads to establish persistent infections in lymphatic tissues has been described previously. These Ads also persistently infect various transformed hematopoietic cell lines in vitro. Our studies indicate that replication of the species B2 Ads is also restricted in cells of hematopoietic origin (both in primary and transformed cells). Taken together, the results indicate that species B2 Ads (as compared to other Ads) seem to enter and infect most hematopoietic cells efficiently, which is in line with the persistent nature of these Ads. They would presumably act as suitable vectors for efficient transduction of most cells of hematopoietic origin, as has already been shown for e.g. HSCs and dendritic cells. The finding that replication of Ads in T-cells appears to depend on the level of T-cell activation, strengthens the hypothesis that T-cells may serve as a reservoir for human Ads and raises possible safety issues for usage of species B-based vectors in hematopoietic cells.

List of papers

Open this publication in new window or tab >>Adenovirus types 11p and 35p show high binding efficiencies for committed hematopoietic cell lines and are infective to these cell lines: ad serotypes with tropism for hematopoietic cells

Open this publication in new window or tab >>There Are Two Different Species B Adenovirus Receptors: sBAR, Common to Species B1 and B2 Adenoviruses, and sB2AR, Exclusively Used by Species B2 Adenoviruses: THERE ARE TWO DIFFERENT SPECIES B ADENOVIRUS RECEPTORS

Abstract [en]

The 51 human adenovirus serotypes are divided into six species (A to F). Many adenoviruses use the coxsackie-adenovirus receptor (CAR) for attachment to host cells in vitro. Species B adenoviruses do not compete with CAR-binding serotypes for binding to host cells, and it has been suggested that species B adenoviruses use a receptor other than CAR. Species B adenoviruses mainly cause disease in the respiratory tract, the eyes, and in the urinary tract. Here we demonstrate that adenovirus type 11 (Ad11; of species B) binds to Chinese hamster ovary (CHO) cells transfected with CD46 (membrane cofactor protein)-cDNA at least 10 times more strongly than to CHO cells transfected with cDNAs encoding CAR or CD55 (decay accelerating factor). Nonpermissive CHO cells were rendered permissive to Ad11 infection upon transfection with CD46-cDNA. Soluble Ad11 fiber knob but not Ad7 or Ad5 knob inhibited binding of Ad11 virions to CD46-transfected cells, and anti-CD46 antibodies inhibited both binding of and infection by Ad11. From these results we conclude that CD46 is a cellular receptor for Ad11.

Abstract [en]

Gene transfer into human hematopoietic stem cells using Ad5 is inefficient due to lack of the primary receptor CAR and the secondary receptors alphavbeta3 integrin and alphavbeta5 integrin, and due to the high seroprevalence of Ad5 antibodies in most adults, resulting in diminished gene transduction. In the present study, we screened six species (species A-F) of adenovirus, displaying different tropisms for interaction with CD34+ cells, at the level of virus attachment and expression. Virus particles were biotinylated and their binding capacity was determined by FACS analysis using streptavidin-FITC. Ad11p, Ad35, and Ad3 (species B) showed high binding affinity, while Ad7, Ad11a (species B), and Ad37 (species D) displayed intermediate affinity. Virions of Ad4 (species E), Ad5 (species C), Ad31 (species A), and Ad41 (species F) hardly bound to hematopoietic progenitor cells. Using a double-labeling system, we demonstrated that adenoviruses bind to quiescent CD34+ cells. Ad11p virions showed the highest affinity among the adenoviruses detected. We further confirmed that virus fiber-specific receptors were present on the hematopoietic progenitor cell surface, because both recombinant fiber of Ad11p and specific antiserum against rfiber could block virus attachment. The ability of the adenoviruses to infect hematopoietic cells was studied by immunofluorescence staining. The adenoviruses from species B and Ad37 showed higher infectivity than Ad31, Ad5, Ad4, and Ad41. Among the studied species B adenoviruses, Ad11p manifested a superior infectivity. Thus, we have confirmed that these cells have high-affinity receptors for species B:2 human adenovirus, Ad11p, and this virus may be used as candidate vector to target therapeutic genes to hematopoietic stem cells.